There are two categories of apparatus designs which are utilized to measure the extent of gas uptake or evolution during a chemical reaction. In one type the pressure of the gaseous reactant or gas evolved is kept constant by changing the volume the gas occupies within the reaction apparatus with the extent of gas consumption or evolution determined by the volume change required to maintain constant pressure. In the second type the volume of the system remains constant and the amount of gas consumed or evolved is determined by the corresponding pressure change. The first type of system is used almost exclusively for reactions conducted at or near atmospheric pressure, while the second type generally is operated at elevated pressures.
Constant pressure systems provide a more meaningful interpretation of reaction results since in such systems the amount of gas present per unit volume remains constant. In constant volume systems the amount of gas available for further reaction is constantly decreasing thus making the evaluation of reaction rate data more complex.
Automation of the constant volume systems is not a factor in equipment design since the only change in the system is the internal pressure, a change which occurs as the gas is either consumed or evolved. Automated recording of this pressure change can be accomplished with a pressure sensing means such as a pressure transducer or similar device within the system which measures the output of the pressure sensing means with time.
Automation of the constant pressure apparatus is more complex. In these systems the pressure is kept constant by using various methods to automatically change the volume of the system as the gas is consumed or evolved. This can be accomplished manually by raising or lowering a levelling bulb filled with a liquid and attached to the bottom of a gas burette by a flexible tube. Automation of such systems has been achieved by the use of a motor driven device to raise or lower the bulb with the motor being regulated by impulses from a pressure sensing device. When the device detects a small pressure change, the motor is actuated and the gas volume is adjusted to regain the original operating pressure. The use of a motor driven threaded metal rod to displace an appropriate volume of gas is described in Chem. and Ind., 1125 (1971).
Another technique is to use a motor driven gas syringe to change the volume of the system as described in publications such as Rev. Sci. Instr., 37, 1734 (1966), and 39, 590 (1968); and Magy. Kem. Foly., 79, 212 (1973). Such an apparatus can be used at elevated pressures as well as atmospheric. The motors employed in these systems are reversible, frequently driven by servo mechanisms and usually attached to a multiturn variable resistor so the gas volume can be electronically recorded. In all of these systems the capacity is determined by the size of the burette or syringe, and it is necessary to change the size of the gas holding device to vary the scale of the reactor.
Other device designs are used to record and control the pressure within a gas reaction apparatus, such as those described in U.S. Pat. Nos. 2,638,919; 4,576,194; and 4,679,583. However, none of these devices have provisions for recording the volume changes associated with the pressure regulation.
All of the known automatic systems generally have both mechanical and electrical features which are difficult to design and build, and which are subject to the wear associated with mechanical systems.
There is continuing interest in the development of improved apparatus designs in which gas consumption or gas evolution during a chemical reaction is measured.
Accordingly, it is an object of this invention to provide a volumetric chemical reaction system which is adapted to conduct and monitor a gas-consuming or gas-evolving reaction.
It is a further object of this invention to provide a chemical reaction system which operates at constant pressure and volume, and has automated means for calculating kinetic parameters and a concentration-time plot from the system data output.
Other objects and advantages of the present invention shall become apparent from the accompanying description and Example, and drawings.